The overall purpose of this study is to determine if there are immune sequelae related to the long-term donation of blood or blood products. Detailed studies of possible immune alterations due to donations are critical in determining safety for donors. The proposed study will investigate many aspects of the immune response which have not been studied in these donors to determine if any alterations occur in long- term donors or develop over time in new donors. The first objective of this study is to investigate changes in immune function which may occur as a result of blood, plasma, or platelet donations. Our preliminary studies have shown evidence of alterations in immune parameters in normal apheresis donors with the most marked changes occurring in long-term plasmapheresis donors. To ascertain whether donation of blood or blood products alters specific immune parameters, we will study WBC receptors known to be involved in normal host defense mechanisms, lymphocyte subpopulations, plasma proteins, and complement activation products from 30 individuals in each of 4 separate donor groups: whole blood donors, bulk plasma donors, plasma donors stimulated with incompatible RBC, and platelet donors. Donor immune data will be compared with results in nondonor controls will also be correlated with demographic data, donation history, laboratory data, and clinical findings. The second objective of this study is to determine if changes in an individual donor's immune status occur over time. A longitudinal study of 15 new donors in each donation group will be performed to evaluate alterations in immune function that may occur in committed donors of blood products and whether there is any clinical significance to the findings. New donors will be enrolled in donation groups and followed longitudinally for a period of up to 2 years.